Poor Mr Gorbachev. Every time he met Ronald Reagan at a summit, he was subjected by the American President to a stream of Russian jokes. Or rather, to be precise, Soviet jokes - the point of which was always to satirise some aspect of life under communism. What made it worse was that some of them really were very funny.

I like the one, for example, about the man who goes to buy a car in Moscow, pays for it, and is told by the salesman that he can collect it on a particular date in 10 years' time. The buyer thinks for a moment and then asks: 'Morning or afternoon?' The salesman, astonished by the question, asks: 'What difference does it make?' And the buyer answers: 'Well, the plumber is coming in the morning.'

As Gorbachev was well aware, these jokes had not been manufactured by some sinister department of the CIA; they were real ones, as told by real Russians. He was probably also aware that although people in the West told jokes about the frustrations of ordinary life, there was no such thing as a whole category of jokes about the capitalist system as such.

If there had been, we can be sure that his aides would have been feeding them to him, contributing to an ever-escalating jokes race between the superpowers.

For some commentators in the 1980s, the existence of this type of humour in the communist world took on a profound significance. It demonstrated the indomitable nature of the human spirit under oppression; the fact that communism produced such a huge quantity of jokes showed how hugely oppressive it was; and the stubborn persistence of this humour played a major role in undermining Soviet rule. In the end, they said, communism was laughed out of existence.

Ben Lewis, a television documentary producer with a good knowledge of Russian and German and an inquisitive but sceptical mind, has set out to test these claims.

He has travelled through the former Soviet bloc, collecting jokes, inspecting police records and interviewing cartoonists, dissidents, politicians and diehard communists. The result is a fascinating book which, while written in a resolutely non-academic style (we learn perhaps a little too much about his bedroom conversations with his East German girlfriend), engages with the existing theories and argues that most of them are wrong. In the process, it also manages to tell a lot of jokes.

Did communism generate an unprecedented amount of humour? Lewis studies the available evidence about humour under Nazism, and concludes that communism certainly did better.

But what exactly does it mean to 'generate' a joke? The precise origins of most jokes are unknown; in some cases, however, it is clear that the joke was recorded long before the birth of the Soviet Union.

Lewis gives a striking example of this: the story of the sheep who try to leave the country, explaining to the border guards that they want to get out because the secret police have received orders to arrest all elephants. 'But you're not elephants.' 'Try telling that to the secret police.' This joke, he discovers, can be found in a 12th-century Persian poem.

(I could add a few more examples. One of his gags, 'Is it true that half the Central Committee are idiots?' 'No, that's rubbish. Half the Central Committee are not idiots,' is a version of a story told about Disraeli: 'Mr Speaker, I withdraw that statement. Half the Cabinet are not asses.' As for the wince-making joke about the Russian announcement that a man would land on the Sun - 'But Mr Brezhnev, the cosmonauts will burn up!' 'Do you take me for a fool? They'll be landing at night!' - I distinctly recall being told that one in a school playground, 40 years ago, about the Irish space programme.)

One of Lewis's findings is obviously true, but interesting none the less: the golden age of joke-telling in the Soviet Union came after Krushchev's 'thaw', when jokes ceased, on the whole, to be imprisonable offences.

Another conclusion is also of interest, but less obviously true: he argues that the regime itself also used humour, and that the joke wars were fought 'between two sides who had both agreed to fight a battle on the terrain of laughter'.

What is the evidence for this? Lewis begins by offering examples of Stalin's sadistic humour, which played on the idea that he was a tyrant and/or a bureaucrat, requiring and at the same time daring his interlocutor to laugh at such a comic notion. This was hardly a battle on a level playing field.

More promisingly, Lewis investigates the 'satirical' magazines published by the regime, and finds that they too contained little jokes about queues, shortages and bribes. Does this mean (as he tends to conclude) that both sides really did occupy the same 'terrain of laughter'?

Ben Lewis does not maintain a doctrine of equivalentism right to the bitter end; he notes that Gorbachev himself, when arguing with his colleagues, used the existence of jokes about the communist system as evidence that the system must be reformed.

But I think he downplays the significance of the most central category of these jokes, the core, the crème de la crème. What they depended on was the inherent absurdity of the official Soviet doctrine, rhetoric and propaganda - not just because it was absurd, but because it was official (in a way that no capitalist doctrine could be).

'What is the difference between communism and capitalism?' 'Capitalism is the exploitation of man by man; communism is the exact opposite.'

'Capitalism stands on the brink of the abyss. It will soon be overtaken by communism.'

'Is it true that Marxism-Leninism is scientific?' 'No, surely not. If it were, they would have tested it on animals first.'

Here, perhaps, we find at long last the jokes that only communism could produce. And while they may not have brought it down, they can still tell us something important about why it fell.